Low inductance unit particularly for electric welders

ABSTRACT

An electric transformer for transforming three-phase power from a three-phase power source into single-phase power. The transformer has a plurality of elongated and parallel shell-type transformer cores with each of the cores having a primary winding and a secondary winding associated therewith. The primary windings have input terminals terminating at one end of the plurality of elongated and parallel shell-type cores. The secondary windings comprise at least one turn associated with each of the shell-type cores with one turn associated with one of the cores being opposite in polarity to the other turns. The opposite ends of the secondary windings terminate at opposite longitudinal ends of the cores.

United States Patent 1 Leathers June 26, 1973 [76] Inventor: Chester F. Leathers, 9326 E. Shore Drive, Portage, Mich. 49081 22 Filed: July 2,1971

21 Appl.No.: 159,274

Related U.S. Application Data [63] Continuation-impart of Ser. No. 25,055, April 2,

1970, abandoned.

[52] U.S. Cl 321/57, 219/116, 323/44, 323/48 [51] Int. Cl. H02m 5/14 [58] Field of Search 321/7, 57, 68; 323/44, 48; 219/116 [56] References Cited UNITED STATES PATENTS 2,666,178 1/1954 Krfmer 321/7 3,099,784 7/1963 Forsha et al. 321/57 X 3,375,429 3ll 9 68 Pagano 321/57 FOREIGN PATENTS OR APPLICATIONS 157,409 10/1963 U.S.S.R 321/57 Primary Examiner-Gerald Goldberg Alt0rney-W0odhams, Blanchard 8L Flynn [57] ABSTRACT An electric transformer for transforming three-phase power from a three-phase power source into singlephase power. The transformer has a plurality of elongated and parallel shell-type transformer cores with each of the cores having a primary winding and a secondary winding associated therewith. The primary windings have input terminals terminating at one end of the plurality of elongated and parallel shell-type cores. The secondary windings comprise at least one turn associated with each of the shell-type cores with one turn associated with one of the cores being opposite in polarity to the other turns. The opposite ends of the secondary windings terminate at opposite longitudinal ends of the cores.

3 Claims, 11 Drawing Figures mgm munzs ms 3. 742.334

sum 1 or s 34 34 E II PAIENIEDJUHZBIQIS 3.742 334 sum k (If 5 LOW INDUCTANCE UNIT PARTICULARLY FOR ELECTRIC WELDERS CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part application of my copending application Ser. No. 25,055, filed Apr. 2, i970, now abandoned.

FIELD OF THE INVENTION This invention relates to an electric transformer and, more particularly, relates to transformer wherein the secondary winding consists of a continuous single conductor associated with three elongated and parallel shell-type transformer cores so that one of the turns of the continuous, single conductor associated with one of the shell-type transformer cores is opposite in polarity to the other turns of the continuous, single conductor associated with the other shell-type transformer cores and wherein opposite ends of the continuous, single conductor terminate at opposite longitudinal ends of the cores.

BACKGROUND OF THE INVENTION Inasmuch as the problems out of which the present invention arose existed with respect to the supplying of electrical power to resistance welding equipment, the following discussion will be set forth in terms of a power supply for resistance welding equipment. However, it will be recognized that other types of high amperage loads such as electroplating or heating will present similar problems so that at least in its broader aspects, this invention will be also applicable thereto. Therefor, it will be understood that the hereinafter following discussion and description will refer to resistance welding solely for illustrative purposes and the use of terminology relating to resistance welding will not be taken as limiting.

One of the problems confronting the manufacturer of resistance welding machines is the provision of the welding transformer in close proximity to the welding electrodes to reduce as much as possible the reactive impedance losses created by the passage of a very high alternating current through a relatively long conductor extending between the welding transformer and the welding electrodes. The magnitude of the problem has in the past appeared to be insurmountable and, as a result, there has been a trend toward the use of rectifiers for converting the alternating current power into direct current-power in an effort to reduce the reactive impedance effects of a high current passing through a relatively long conductor between the welding transformer and the welding electrodes.

It has also been found that there are certain uses of electrical resistance welding equipment where a relativcly longer unidirectional current pulse is desired than can be obtained from conventional single-phase power supply apparatus. This has for a long time in the past been solved by the use of three-phase power supply equipment and such is well recognized by the industry. However, previously known equipment of this type has generally been incapable of balancing the phases with respect to each other and, more particularly incapable of insuring that the conductors carrying each of the phases simultaneously present identical impedances to the flow of the welding current. While balanced circuits, as such, have 'been known previously, the ones relating to the supply of welding current with which I am acquainted have been too expensive and/or inconvenient to manufacture or use to make an acceptable commercial product.

Another of the more important problems facing a manufacturer of a resistance welding machine is to minimize the reactive impedance in the secondary circuit. The magnitude of the reactive component of the impedance depends on three things: (1) the frequency of the alternating current; (2) the geometry or pattern of the secondary circuit; and (3) the presence, amount and position of magnetic materials in or near the secondary loop of the machine. In other words, the reactive component of the impedance of the secondary circuit depends on the throat depth, the throat height, proximity of magnetic materials and the frequency of the supply current. If any attempt is made in the design of resistance welding machines to control either the resistive component or the reactive component of the impedance in the secondary circuit, extreme care has to be taken to be sure that a reduction in the resistive component will not effect an increase in the reactive component of the impedance. As a general rule, the throat depth is made as small as possible. However, the throat depth is controlled by the work.

Accordingly, an elongated conductor-like element which may be located in the throat of a resistance welding machine and extend between the welding transformer and the welding electrodes without resulting in high reactive losses in the secondary circuit will be highly desirable.

Accordingly, the objects of this invention include:

1. To provide a three-phase to single-phase transformer power supply unit for supplying a high amperage load wherein the transformer assembly is an elongated conductor-like member and wherein the input terminals to the primary windings are located at one end of the conductor-like member and the output terminals of the secondary winding are located at opposite ends of the conductor-like member.

2. To provide a transformer, as aforesaid, which is particularly applicable to supplying the welding electrodes of an electric resistance welding machine.

3. To provide a transformer, as aforesaid, which is sufficiently compact as to be readily mountable within the arms of a resistance welding machine of conventional size.

4. To provide a transformer, as aforesaid, wherein the distance between the secondary terminal and the welding electrodes is minimized so as to practically eliminate the reactive component of the impedance in the current path in a resistance welding machine.

5. To provide a transformer, as aforesaid, wherein the transformer ratio in the conductor-like member may be sufficient to permit the substitution of a conventional autotransformer for a conventional welding transformer so that the unbalanced conditions generated by the conductor-like member may be balanced by the use of the autotransformer.

6. To provide a transformer, as aforesaid, wherein the transformer ratio in the conductor-like member and the transformer ratio of the conventional welding transformer or autotransformer may be combined to accomplish the desired ratio between the three-phase source and the load.

Other objects and purposes of this invention will be apparent to persons acquainted with apparatus of this general type on reading the following specification and inspecting the accompanying drawings, in which:

FIG. 1 is a schematic illustration of a resistance seam welding machine having incorporated therein a plurality of transformers embodying the invention;

FIG. 2 is a schematic circuit diagram of a conventional transformer incorporated into the transformer of this invention;

FIG. 3A is a schematic illustration of the interconnection of one transformer group to a welding transformer;

FIG. 3B is a schematic illustration of two interconnected transformer groups;

FIG. 3C is a schematic illustration of two interconnected transformer groups with one of the groups having schematically illustrated multiple turns;

FIG. 4 is a sectional view taken through an assembled core arrangement;

FIG. 5 is a schematic circuit diagram of a further embodiment;

FIG. 6 is a schematic illustration of the further embodiment;

FIG. 7 is a sectional view taken along the line VII- -VII of FIG. 6;

FIG. 8 is a schematic illustration of a further embodiment; and

FIG. 9 is a perspective view of the transformer schematically illustrated in FIG. 8.

Certain terminology will be used in the following descriptive material for convenience in reference only and will not be limiting. The words up," down, right and left will designate directions in the drawings to which reference is made. The words in and out will refer to directions toward and away from, respectively, the geometric center of the device and designated parts thereof. Such terminology will include derivatives and words of similar import.

SUMMARY OF THE INVENTION The objects and purposes of the invention are met by providing a transformer for transforming three-phase power from a three-phase source into single-phase power having a plurality elongated and parallel shelltype transformer cores, each core having a primary winding and a secondary winding associated therewith. The input terminals to the primary windings are located at one end of the transformer cores while the output terminals of the secondary windings are located at opposite longitudinal ends of the transformer cores.

DETAILED DESCRIPTION Inasmuch as the problems out of which the present invention arose existed with respect to the supplying of electrical power to resistance welding equipment, a resistance welding machine 10 is illustrated in FIG. 1. The resistance welding machine 10 comprises a frame 11 and a conventional three-phase welding transformer 12 mounted in a conventional manner on the frame 11 and receiving three-phase power from input lines L1, L2 and L3 and delivering converted, three-phase power through lines S1, S2 and S3. The resistance welding machine 10 further comprises a pair of horns or arms 13 and 14 extending outwardly from the frame 11. A pair of welding electrodes 16 and 17, here rollertype welding electrodes, are rotatably supported at the outer ends of the arms 13 and 14 in a conventionally known manner. The zone 18 between the arms 13 and 14 is commonly referred to as the throat of the resistance welding machine 10. The throat depth has been indicated by the reference character K in FIG. 1. In this particular embodiment, the frame 11 is mounted for lateral horizontal movement to move the electrodes 16 and 17 across a workpiece W, such as a pair of relatively wide sheet metal strips, supported on a base 19.

The output lines S1, S2 and S3 from the welding transformer 12 are connected, in this particular em bodiment to the primary windings of three elongated, conductor-like transformers 21, 22 and 23 which embody the invention. While the primary windings of the transformers 21, 22 and 23 are shown to be connected in parallel, they can be connected in series, if desired. It is to be recognized, of course, that the utilization of the transformer 22 may be eliminated and the resistance welding machine 10 will operate satisfactorily with only the transformers 21 and 23. The transformers 21 and 23 are each mounted within one of the arms 13 and 141 and preferably extend the full length of the arms.

FIG. 2 illustrates an electrical circuit diagram for the transformers 21 and 23 illustrated In FIG. 1. Since the transformers 21, 22 and 23 are identical, only the transformer 21 will be discussed in detail. The components of the remaining transformers 22 and 23 will be referred to by the same reference numerals designating corresponding components of the transformer 21 but with the suffixes A and B added thereto, respectively.

The transformer 21 (FIGS. 2, 3A and 3B) comprises two transformer groups and 121, each group having three elongated, hollow shell-type cores 126, 127, 128, 26, 27 and 28 extending parallel to each other. Each core in each group has a primary winding and a secondary winding associated therewith. In this partic ular embodiment, the primary winding 129 and the secondary winding 131 are associated with the core 126. The primary winding 132 and the secondary winding 133 are associated with the core 127. The primary winding 134 and the secondary winding 136 are associated with the core 128. The primary windings 129, 132 and 134 are connected to the lines S1, S2 and S3. The primary windings 129, 132 and 134 are connected in a commonly known wye (or star) connection. The secondary windings 131, 133 and 136 are also connected in a wye connection. The primary winding 29 and the secondary winding 31 are associated with the core 26. The primary winding 32 and the secondary winding 33 are associated with the core 27. The primary winding 34 and the secondary winding 36 are associated with the core 28. The primary windings 29, 32 and 34 are connected in a commonly known wye (or star) connection. The output of the secondary windings 131, 133 and 136 are connected to the input to the primary windings 29, 32 and 34, respectively. The neutrals of each of the transformer groups 120 and 121 are located on the same end of the cores and are connected together through a line 122 to form an interconnected star so that a balanced three-phase system will be achieved. The secondary windings 31, 33 and 36 are series connected to each other between the output terminals 37 and 38 with the secondary winding 33 being connected oppositely to the secondary windings 33 and 36 so that the voltage appearing between the terminals 37 and 38 will be twice that of each transformer secondary winding. The secondary windings of each of the transformer groups 121, 121A and 121B of the transformers 21, 22 and 23, respectively, are series connected with each other between the electrodes 16 and 17.

The elongated hollow shell-type cores 126, 127, 128, 26, 27 and 28 (FIGS. 3A, 3B and 4) are separated by conventional insulation material 40. The primary windings 129, 132 and 134, 29, 32 and 34 of the transformer groups 120 and 121 (as well as the transformer groups in the transformers 22 and 23) each comprise a single conductor of sufficient size to carry the required current. The secondary windings 131, 133, 136, 31, 33 and 36 also comprise a single conductor of sufficient size to carry the required current. In the transformer group 120, the primary winding 129 and the secondary winding 131 extend through the center of the shell-type core 126 and are separated by conventional insulation material 139. Similarly, the primary winding 132 and the secondary winding 133 extend through the center of the shell-type core 126 and are separated by conventional insulation material 139. Similarly, the primary winding 132 and the secondary winding 133 extend through the center of the shell-type core 127 and are separated from each other by insulation 141. The primary winding 134 and the secondary winding 136 extend through the center of the shell-type core 128 and are separated from each other by insulation material 142.

In the transformer group 121, the primary winding 29 and the secondary winding 31 extend through the center of the shell-type core 26 and are separated by conventional insulating material 39. Similarly, the primary winding 32 and the secondary winding 33 extend through the center of the shell-type core 27 and are separated from each other by insulation 41. The primary winding 34 and the secondary winding 36 extend through the center of the shell-type core 28 and are separated from each other by insulation material 42. The secondary windings 31, 33 and 36 are further connected so that the output terminals 37 and 38 are located at opposite longitudinal ends of the cores 26, 27 and 28.

Thus, the utilization of the transformer 21 in the arm 13 of a resistance welding machine is most advantageous since the output terminal 38 of the secondary winding of the transformer 21 is located closely adjacent the electrode 16 and the output terminal 37 of the secondary winding is located closely adjacent the inner end of the throat of the resistance welding machine 10. This permits a connection of the output terminal 37A and 38A of a similar type transformer 22 to the output terminals 37 and 38B of the transformers 21 and 23, respectively, so that the secondary windings of each of the transformers 21, 22 and 23 will be series connected between the electrodes 16 and 17.

The transformer 21C illustrated in FIG. 3C is essentially identical to the transformer 21 illustrated in FIG. 3B and accordingly, the same reference numerals have been used to indicate the corresponding components of the transformer 21 except that the suffix C has been added. The primary difference between the transformer 21 and the transformer 21C is that the primary windings 129C, 132C and 134C can be wound with multiple turns. Thus, the welding transformer 12 can be eliminated with a proper number of turns being provided in the primary windings 129C, 132C and 134C. The secondary windings 131C, 133C and 136C of the transformer group C and the primary windings 29C, 32C and 34C and secondary windings 31C, 33C and 36C of the transformer group 121C are the same as the embodiment illustrated in FIG. 3B.

Referring now to FIGS. 5 through 7, the welding transformer 12A is similar to the welding transformer 12 illustrated in FIGS. 2 through 4 except that the windings of the transformer are connected delta-Wye. The transformer 46 comprises only one transformer group in contrast to the transformer 21 illustrated in FIGS. 2 through 4 which has two transformer groups. The primary windings are connected in a three-phase connection known as a zigzag or interconnected star connection. This connection is obtained by providing on each core of the transformer two equal primary windings. In other words, and referring to FIG. 5, a pair of equal primary windings 47 and 48 are provided on the core 49. A pair of equal primary windings 51 and 52 are provided on the core 53 and a pair of equal primary windings 54 and 56 are provided on the core 57. The zigzag winding for one phase is obtained by connecting one primary winding from one core in series with one of the primary windings of another core. Thus, the primary winding 47 is connected in series with the primary winding 52 on the core 53. The primary winding 48 on the core 49 is connected in series with the primary winding 54 on the core 57 and the primary winding 51 on the core 53 is series connected with the primary winding 56 on the core 57. One of the most common uses of this type of zigzag connection is to provide a grounded neutral 58 on an otherwise ungrounded system. Thus, an interconnecting of the neutral on the secondary of the welding transformer 12A and the neutral of the interconnected star as at 58, a balanced threephase system will be achieved.

The secondary winding 59 associated with the core 49, the secondary winding 61 associated with the core 53 and the secondary winding 62 associated with the core 57 are connected in series with each other so that one of the secondary windings, here the secondary winding 61, is connected oppositely to the remaining secondary windings 59 and 62 as discussed above in relation to the FIGS. 2 through 4 embodiment. Further, the secondary windings 59, 61 and 62 are connected in series with each other between the output terminals 63 and 64.

The cores 49, 53 and 57 are each comprised of an elongated, hollow shell. Each of the hollow shells are placed in a side-by-side manner separated from each other by insulation 66. The primary windings 47 and 48 and the secondary winding 59 each comprise a single conductor, each having a size sufficient to carry the required high magnitude of current. The single primary and secondary conductors, 47, 48 and 59, respectively, extend through the center of the shell-type core 49 and are separated from each other by insulation 68. Similarly, the primary windings 51 and 52 and the secondary winding 61 comprise a single conductor having a sufficient size to carry the required high current. The single conductors 51, 52 and 61 extend through the center of the hollow shell-type core 53 and are separated from each other by insulation 69. The primary windings 54 and 56 and the secondary windings 62 also comprise a single conductor having a sufficient size to carry the required high current. The simple conductors 54, 56 and 62 extend through the center of the hollow shell-type core 57 and are separated from each other by insulation 71. The primary windings 47, 48, Si, 52, 54 and 56 are connected as illustrated in the electrical circuit diagram of FIG. and described above. The single turn secondary windings 53, 61 and 62 are connected in series with each other with one of the secondary windings, here secondary winding 61, connected oppositely from the remaining two secondary windings. The output terminals 63 and 64 of the secondary winding of the transformer 46 are located at opposite longitudinal ends of the cores 49, 53 and 57.

Alternatively, if desired, the welding transformer 12A illustrated in FIGS. 5 and 6 can be replaced with an autotransformer assembly 67 illustrated in FIG. 8. However, and since the primary windings are connected directly to the lines L1, L2 and L3, this means that the transformer 46A must contain multiple primary windings in order to provide a sufficient stepdown transformer ratio to develop the desired current level. The transformer 46A is connected in the commonly known zigzag or interconnected star connection as illustrated in FIG. 5 to provide a low impedance neutral 58A. Accordingly, the components of the transformer 46A will be referred to by the same reference numerals designating corresponding components of the transformer 46 but with the suffix A added thereto and will not, therefore, be discussed in detail.

The autotransformer assembly 67 comprises a threephase autotransformer consisting, if desired, of three single-phase autotransformers 67A, 67B and 67C which are connected in a zigzag or interconnected star connection to provide a low impedance neutral point 588. When the neutral 58B is connected to the neutral point 58A, the unbalanced condition in the three-phase system generated by the transformer 46A will be balanced.

FIG. 9 illustrates one embodiment of the transformer 46A wherein multiple turn primary windings and a single turn secondary winding is provided with each core 46A, 53A and 57A. Since less current is carried in the primary windings the cross-sectional area of the conductors may be considerably smaller to permit a large number of turns to pass through the centers of each of the cores.

In all of the above described transformer constructions and any modifications thereof within the scope of the claims of this application, conventional heat control and/or voltage regulation in accordance with the practice of the art may be applied without disadvantageous effects on their operation. If desired, the zigzag or interconnected star connection of the autotransformer assembly 67 in FIG. 8 can be replaced with a conventional autotransformer which, if desired, can be tapped to provide a desired voltage regulation.

OPERATION The operation of the transformers described hereinabove will be understood by skilled persons since all of the transformers constructions comply withconventional and well known transformer theory. Accordingly, no further description of such operation is believed necessary.

It will be immediately recognized that by providing a plurality of any of the foregoing transformers in a resistance welding machine 10, the reactive component of the impedance will be virtually eliminated due to the 6 fact that the transformers 21 and 23, which transformers may be replaced with transformers 36 and 46A, are

mounted in the arms 13 and 14 of the resistance welding machine 10. Thus, the power factor will approach unity with the well understood advantages thereof. Since the output terminals of the secondary windings of each of the transformers are located at opposite ends of the core assembly, the transformers 21, 22 and 23 may be connected end-to-end so that almost all of the secondary circuit is inside the transformer cores. This unique arrangement is particularly desirable in resistance welding machines.

In the foregoing described and illustrated embodiments, the primary winding connections are all at the same end of a given arm transformer, as the transformer 21 or the transformers 46 and 46A. While this is desirable, especially where the primary winding has only a few turns, where more turns, as 15 or more, are used, the connections may, if desired, be at both ends without seriously, if at all, affecting the operation of the system.

Although particular preferred embodiments of the invention have been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

ll. In a transformer for transforming three-phase power from a three-phase source into single-phase power, the combination comprising:

a pair of transformer groups, each transformer group having a plurality of elongated and parallel shelltype transformer core means;

a primary winding associated with each of said core means in said pair of transformer groups, each of said primary windings of one of said transformer groups having an input connectible to said three phase power source;

a first secondary winding associated with each of said core means in said one of said transformer groups and having an output connected to the input to the primary windings in the other of said transformer groups;

a secondary winding in said other transformer group comprising at least one turn associated with each of said core means in said other transformer group, said secondary windings being connected so that one of said secondary windings associated with one of said core means is opposite in polarity to another of said secondary windings, opposite ends of said secondary winding being located at opposite longitudinal ends of said core means.

2. The transformer defined in claim I, wherein said first secondary winding is connected in a wye connec tion with the neutral point located at one of said core means of said one transformer group; and

wherein said primary windings of said other transformer group are connected in a wye connection with the neutral point located at the same end of said core means is said first mentioned neutral point; and

including conductive means connecting said two neutral points.

3. The transformer defined in claim I, wherein said primary windings in said one transformer group include multiple turns. 

1. In a transformer for transforming three-phase power from a three-phase source into single-phase power, the combination comprising: a pair of transformer groups, each transformer group having a plurality of elongated and parallel shell-type transformer core means; a primary winding associated with each of said core means in said pair of transformer groups, each of said primary windings of one of said transformer groups having an input connectible to said three phase power source; a first secondary winding associated with each of said core means in said one of said transformer groups and having an output connected to the input to the primary windings in the other of said transformer groups; a secondary winding in said other transformer group comprising at least one turn associated with each of said core means in said other transformer group, said secondary windings being connected so that one of said secondary windings associated with one of said core means is opposite in polarity to another of said secondary windings, opposite ends of said secondary winding being located at opposite longitudinal ends of said core means.
 2. The transformer defined in claim 1, wherein said first secondary winding is connected in a wye connection with the neutral point located at one of said core means of said one transformer group; and wherein said primary windings of said other transformer group are connected in a wye connection with the neutral point located at the same end of said core means is said first mentioned neutral point; and including conductive means connecting said two neutral points.
 3. The transformer defined in claim 1, wherein said primary windings in said one transformer group include multiple turns. 